Anticavitation device

ABSTRACT

A flow separator is placed along the axis of a vertical duct and has a radial enlargement which is in contact with the internal duct wall. The duct is thus separated into a lower region and an upper region in which are located orifices for the admission of liquid under pressure. The radial enlargement is provided with an upward tubular extension which is so shaped internally as to form a highly progressive convergent-divergent nozzle while defining externally with the duct wall an annular space having at least one section which is partially throttled by a transverse diaphragm, said diaphragm being rigidly fixed to said tubular extension.

United States Patent Constantin et al. 1 Jan. 23, 1973 [541ANTICAVITATION DEVICE 1,419,876 6/1922 Mefelsden etal. ..138 44 [75]Inventors: Je n Pierre C ntin Grenoble; 1,802,766 4/l93l Kerr ..l38/44Jean-Claude Duquesne; Michel Pontier, both of Aix en Provence, PrimaryEXami'lerHel'bel't R055 l f France Attorney-Cameron, Kerkam & Sutton[73] Assignee: Commissariat A LEnergie Atomique, Paris, France [57]ABSTRACT [22] Fiied; Jam 19 7 A flow separator is placed along the axisof a vertical duct and has a radial enlargement which is in contact [21]PP N05 107,744 with the internal duct wall. The duct is thus separatedinto a lower region and an upper region in which are [30] ForeignApplication Priority Dam located orifices for the admission of liquidunder pressure. The radial enlargement is provided with an up- Feb. I3,1970 France ..700527l ward tubular extension which so shaped internallyas to form a highly progressive convergent-divergent [52] US. Cl..l38/44 nozzle while defining externally with the duct wall an Cl 6 l/0annular space having at least one section which is par- [581 Field ofSearch ..l38/39, 40, 44 tially throttled by a transverse diaphragm, saiddiaphragm being rigidly fixed to said tubular exten- [56] ReferencesCited sion.

UNITED STATES PATENTS 2 Claims, 1 Drawing Figure 1,298,47l V 3/1919D0dge.... .l38/44 X ANTICAVITA'IION DEVICE This invention relates to adevice for limiting and if necessary even eliminating the phenomenon ofcavitation within a duct which is supplied with a liquid under pressurethrough orifices formed in different regions in the lateral surface ofsaid duct, the jets of liquid which are derived from said orifices beingliable to induce turbulences in the flow regime in the zones in whichsaid jets meet when provision is not made for the device underconsideration.

The invention applies primarily although not exclusively to nuclearreactor fuel assemblies, especially fuel assemblies which are cooled bya liquid such as liquid sodium and which usually comprise a cylindricalendfitting located in a vertical position during use within the reactor;the sodium passes into said end-fitting through lateral orifices whichare disposed in a number of horizontal rows provided at different levelsand undergoes an abrupt deviation substantially at right angles, thenflows upwards in the direction of the fuel pins of the assembly whichare mounted above the endfitting. Said end-fitting plays the part of amechanical support and also has a hydraulic function. Experience hasshown that the phenomenon of cavitation in the coolant appearsespecially at the level of the upper orifices at the point of contactwith the upward flow which comes from the lower orifices. As a result ofthis phenomenon, the assembly is liable to be attended by majordisadvantages such as erosion of certain structures, production of highnoise arising from resorption of bubbles produced within the liquid,thereby preventing the operation of acoustic devices for detectingsodium boiling and finally the possible presence of vibrations which areliable to cause damage to some parts of the assembly and to impair themechanical strength of the structure as a whole.

The aim of this invention is to provide a device which overcomestheabove-mentioned disadvantages, especially by preventing any contactbetween the jets of liquid which pass out of the upper orifices and theflow which is derived from the lower orifices.

To this end, said device essentially comprises a flowseparatingcomponent which is placed along the axis of the vertically disposed ductand has a radial enlargement which is in contact with the internal wallof the duct so as to separate said duct into a lower region and an upperregion in which are located orifices for the admission of a liquid, saidenlargement being provided with an axial extension in the upper regionin the form of a tubular casing having internally the shape of aconvergent-divergent nozzle with very progressive inlet and outletprofiles and defining externally with the duct wall an annular spacehaving at least one section which is partially throttled by a transversediaphragm, said diaphragm being rigidly fixed to said tubular casing.

As an advantageous feature and in a preferred embodiment of theinvention, the tubular casing comprises a cylindrical extension having awall which is parallel to the duct, the transverse diaphragm beingplaced at the point of junction of said casing and said extension.

Further properties of the anticavitation device considered will becomeapparent from the following description of one exemplified embodimentwhich is given by way of indication without any limitation beingimplied, reference being made to the single FIGURE of the accompanyingdrawings in which the extremity of a t fuel-assembly end-fittingprovided with a flow separator in accordance with the invention isillustrated diagrammatically in axial cross-section.

In this FIGURE, the reference numeral 1 generally designates theend-fitting of a fuel assembly for nuclear reactors and especiallyreactors of the so-called fast neutron type in which the core is cooledby a continuous circulation of liquid metal such as sodium. Saidend-fitting l is provided in the form of a cylindrical duct having avertical axis and constituted by a side wall 2 and an end-cap 3 whichserves to close said wall at the lower extremity. The end-fitting l isopen at the upper extremity and joined to the fuel assembly proper (notshown in the FIGURE) which contains in particular pin-type elementsformed of suitable nuclear fuel material. In order to permit efficientcooling by means of the sodium which flows through the fuel assembly,the end-fitting l is provided with a series of radial orifices which areformed through the wall 2 and designated in the FIGURE by the referencenumerals 4 and 5 according as said orifices are located at the bottomportion or top portion of the end-fitting. Said orifices 4 and 5 arepreferably arranged in a number of superposed horizontal rows eachconsisting of a given number of orifices such as six in the embodimentwhich is shown byway of example in the FIGURE. The sodium under pressurewhich thus penetrates into the endfitting after having passed throughthe above-mentioned orifices undergoes an abrupt deviation substantiallyat right angles as shown by the arrows 6, then flows upwards within theend-fitting in the direction of the fuel assembly as shown by the arrow7.

The higher performances which are required from nuclear reactor fuelassemblies especially in order to obtain higher power levels, highertemperature levels and higher flow rates entail the need for higherrates of flow of the coolant sodium. In practice, this results inincreased danger of cavitation, in particular at the level of theorifices which are formed in the upper portion or region of theend-fitting.

In order to prevent the appearance of this phenomenon, provision is madein accordance with the invention for a flow-separating component whichis mounted within the interior of. the fuel-assembly endfitting anddesignated in the drawing by the reference numeral 8. Saidflow-separating component is provided at one extremity with anenlargement 9 which serves to secure the flow separator to the internalsurface of the end-fitting wall 2 and separates said end-fitting into anupper region and a lower region. The component 8 also has a tubularcasing 10 which is provided internally with a flow cross-section havingthe shape of a convergent-divergent nozzle with very progressiveprofiles 11 and 12 respectively. At the end which is remote from theenlargement 9, the convergent-divergent portion 12 is joined to acylindrical extension 13 which is coaxial with the wall 2. The assemblywhich is formed by the tubular casing 10 and the extension 13 defines anannular space 14 with the wall 2 and the sodium derived from theorifices 5 of the upper region flows into said space, the sodium streambeing thus completely separated from the stream which flows from theorifices 4. The component 8 thus provides total separation between thestreams derived from the orifices mentioned above while making itpossible in particular to prevent said streams from coming into contactwith each other and thus developing turbulences. Beyond the extension13, the fluid jets are parallel and are mixed without giving rise to anycavitation phenomenon.

Moreover, in order to ensure substantially greater uniformity in theflow velocities of the fluid jets which are derived from the differentorifices, the flow separator 8 is advantageously provided with atransverse diaphragm within the annular space 14 at the point ofjunction of the divergent portion 12 and the extension 13. The designfunction of said diaphragm 15 is to produce an appreciable obstructionwithin said space 13 and to increase the gain which results from theseparator itself.

It will have become quite clear from the foregoing that the invention isnot limited to the exemplified embodiment as hereinabove described withreference to the accompanying FIGURE but extends to all alternativeforms.

What we claim is:

1. An anticavitation device comprising a duct having a plurality oforifices for admitting a liquid under pressure into said duct, aflow-separating component having an annular enlargementcircumferentially secured to the internal wall of the duct so as toseparate said duct into a lower region and an upper region in which theorifices for the admission of the liquid are located, said enlargementhaving an axial extension in the upper region in the form of a tubularcasing having internally the shape of a convergent-divergent nozzle withvery progressive inlet and outlet profiles, said tubular casing definingan annular space with the duct wall and having a transverse diaphragmrigidly fixed to said tubular casing for throttling the flow in saidannular space.

2. An anticavitation device according to claim 1, wherein the tubularcasing includes a cylindrical extension having a wall which is parallelto the duct, the transverse diaphragm being placed at the point ofjunction of said casing and said cylindrical extension.

1. An anticavitation device comprising a duct having a plurality oforifices for admitting a liquid under pressure into said duct, aflow-separating component having an annular enlargementcircumferentially secured to the internal wall of the duct so as toseparate said duct into a lower region and an upper region in which theorifices for the admission of the liquid are located, said enlargementhaving an axial extension in the upper region in the form of a tubularcasing having internally the shape of a convergent-divergent nozzle withvery progressive inlet and outlet profiles, said tubular casing definingan annular space with the duct wall and having a transverse diaphragmrigidly fixed to said tubular casing for throttling the flow in saidannular space.
 2. An anticavitation device according to claim 1, whereinthe tubular casing includes a cylindrical extension having a wall whichis parallel to the duct, the transverse diaphragm being placed at thepoint of junction of said casing and said cylindrical extension.